Automated determination of germination time courses by image capture and early counts of radicle emergence lead to a new vigour test for winter oilseed rape (Brassica napus)

The objective of the work was to develop a routine vigour test indicative of the relative field emergence of commercial seed lots of winter oilseed rape. The potential for a vigour test based on rate of radicle emergence (RE) was examined. The germination progress curves of nine lots (cv. Vision) were determined at 20 degrees C using an automated system which captured RE images every two hours for 72 hours. Each curve was described by its mean germination time (MGT), which is the average lag period (delay) from the start of imbibition to RE. MGT was indicative of 7-day field emergence (R-2 = 0.930) and maximum emergence of the lots (R-2 = 0.745). The automated single counts suggested that the 24- and 30-hour counts were the appropriate timings for comparisons across three laboratories in standard germination tests in pleated paper at 20 degrees C. The mean counts, particularly those at 30 hours, from the three laboratories predicted MGT (R-2 = 0.920), 7-day emergence (R-2 = 0.961) and maximum emergence (R-2 = 0.713). A similar ranking of the lots in terms of their RE counts was seen at 13 degrees C after 48 hours in rolled towels. The counts were reproducible between laboratories, all R-2 between laboratories being greater than 0.930. The time to RE was closely related to total germination after controlled deterioration, which gives a measure of seed age. The possibility that the slow rate of RE in low vigour seed may result from more time being needed for repair of deterioration in aged seeds is discussed. A routine vigour test at 20 degrees C in which RE is counted at 30 hours, possibly in a standard germination test, is suggested. Counts of RE could be done either manually or by an automated system such as the one described.